The present invention relates to an image data compression transmission method which uses arithmetic code used in image transmission in facsimile apparatuses and the like, compress and transfer of image data, and more particularly uses decoding error control process when errors occur in data transmission.
Arithmetic coding is one method for the coding of image signals. Arithmetic coding achieves a high coding efficiency without enlarging the information source which generates the information strings to be coded. Arithmetic coding has been described in Japanese Patent Laid-open 222576-1989.
The above arithmetic coding method, called QM-coder, is the standard CCITT recommendation until march 1993. The QM-coder performs of the image data coding process while it estimates a non-priority symbol appearance probability (in general, black picture element in the monotone image) dynamically. It is necessary to determine real non-priority symbols so as to obtain coding efficiency. However, the real non-priority symbol appearance probability is obtained for calculations after all of the picture elements for coding are discovered. Accordingly, when using the scanning method in the facsimile apparatus it is impossible to calculate the real non-priority symbol appearance probability, because the coding processing is coded by mean of scanning image data. Accordingly, the QM-coder sets an initial value of the symbol appearance probability, and estimates non-priority symbol appearance probability dynamically.
The following is a description of the procedures in an image data compression and transmission method using the arithmetic coding (QM-coder).
1 P is set as a non-priority symbol appearance probability of signals that are picture element strings generated from an information source, predetermined parameter A is used, and parameters A.sub.0 and A.sub.1, set beforehand, are used. The parameters A.sub.0, A.sub.1, which satisfy the following equation, are then determined. EQU A.sub.1 =A.times.P, A.sub.0 =A-A.sub.1
2 The codes of picture elements are determined by using parameters A.sub.0 and A.sub.1 described above, and the code C with respect to the picture element string, according to the value of picture element x of an information string that is the object of coding. In addition, one of the parameters A.sub.0 and A.sub.1 is then coded in order by the coder as a new parameter.
3 The coded data is transmitted to the receiving side, and the decoder in the receive side decodes the input coded data into image signals.
The QM-coder characteristic differs from the MH, MR, and MMR methods, in that it does not utilize a page-end code. Accordingly, when the receive side reproduces image data, it is necessary for the transmission to have transmitted all line information of the image data to the receive side. Furthermore, the QM-coder often does not output the code while one line is being coded. Because, when non-priority symbol appearance probability is high, image data code is not generated.
When an image data compression and transmission method using the arithmetic coding is used to perform data transmission, it is a necessary condition that there be no qualitative errors in the code on the transmission line. This condition is the same as a condition in the CCITT recommendations for the T.6 (MMR) method.
For example, if a data transmission error on the transmission line occurs when arithmetic coding is being used to transmit data to the receiving side, a decoder of the receiving side will encounter difficulties in performing decoding of data after that data has been received. As a result, the decoder will not be able to correct errors and decoding will not be possible. Therefore, image data compressed using arithmetic coding will be reproducible only when there are no errors on the transmission line but will not be reproducible when errors are generated on the transfer path. Thus, errors generated on a transfer path limit the compression and transfer of data when using arithmetic coding.